Transplantation systems such as organ transplantations and bone marrow reconstitution have become important and effective therapies for many life threatening diseases. However, immune rejection is still the major barrier for successful transplantation. This is manifested in functional deterioration and graft rejection in the case of organ transplantation (host-versus-graft disease, or HVGD). Another manifestation of pathological immune reactivity is graft-versus-host disease (GVHD) that occurs in approximately 30% of bone marrow recipients. Up to half of those patients who develop GVHD may succumb to this process. This high morbidity and mortality has led to continuous interest in the possibility of controlling or preventing GVHD.
Clinicopathologically, two forms of GVHD have been recognized. Acute GVHD develops within the first 3 months after bone marrow transplantation and features disorders of skin, liver and gastrointestinal tract. Chronic GVHD is a multiorgan autoimmune-like disease, emerging from 3 months up to 3 years post-transplantation and shares features common to naturally occurring autoimmune disorders, like systemic lupus erythematosus (SLE) and scleroderma.
Current available approaches for prevention of GVHD and HVGD include the use of non-specific immunosuppressive drugs, such as cyclosporine, FK506, methotrexate and/or prednisone. However, these treatments induce severe side effects, including nephrotoxicity, hypertension, hypercholesterolemia, diabetogenic effects, neurotoxicity, hirsutism and gengival hyperplasia. Moreover, the unselective depression of the entire immune system renders patients vulnerable to infections. Despite chronic administration of immunosuppressive agents, transplantations have limited success as a therapeutic approach for long term survival. Given these limitations, traditional immunosuppressive therapies cannot overcome the rejection of HLA unmatched transplants and xenografts. Hence, these traditional therapies do not solve the problem of the acute and growing shortage of human donors.
The pathological process of immune rejection is mediated by T-cells that recognize alloantigens presented on self major histocompatibility complex (MHC) molecules, as non-self. They then proliferate, secrete cytokines, and recruit additional inflammatory and cytotoxic cells (Sykes et al., 1996). In MHC matched bone marrow transplantation, GVHD is caused by the competent donor T cells reacting against minor histocompatibility antigens of the recipient. The donor T cells are sensitized to such alloantigens and then directly, or through secondary signals, attack the host cells. In order to prevent immune rejection, it is therefore essential to inhibit antigen presentation and consequently T-cell activation. It has been demonstrated that small synthetic peptides of 11–14 amino acids with high binding affinity for specific class II MHC molecules, were capable of preventing murine graft-versus-host disease (Schlegel et al., 1994). This approach, however, has been limited by the need for allelic specificity of the inhibitor peptides to the MHC haplotype of the donor/recipient, as well as by the difficulty of achieving sustained tissue levels of such low molecular weight peptides over a prolonged period of time.
A high molecular weight synthetic basic random copolymer consisting of L-Ala, L-Glu, L-Lys and L-Tyr residues in the molar ratio of about 6 parts Ala to 2 parts Glu to 4.5 parts Lys to 1 part Tyr, and having a molecular weight of 15,000–25,000, was first described in U.S. Pat. No. 3,849,550 as an agent for treatment or prevention of experimental allergic encephalomyelitis (EAE), a disease resembling multiple sclerosis (MS) that can be induced in susceptible animals. Batches of this copolymer of average molecular weight 23,000, designated Copolymer 1 or Cop 1, were shown to be highly effective in protecting and suppressing EAE in several animal species (Teitelbaum et al., 1971, 1974a, 1974b).
D-Copolymer 1 or D-Cop 1, in which the four amino acids have the D-configuration, namely a random copolymer containing the D-Ala, D-Glu, D-Lys and D-Tyr residues, has also been described (Webb et al., 1976).
Later, Cop 1 was found to significantly reduce the number of relapses in patients with the exacerbating-remitting form of MS (Bornstein et al., 1990; Sela et al., 1990; Johnson et al., 1994). Copolymer 1, in the form of the acetate salts of synthetic polypeptides containing L-Glu, L-Ala, L-Tyr and L-Lys with an average molar fraction of 0.141, 0.427, 0.095 and 0.338, is the active ingredient of COPAXONE®, a medicament for the treatment of multiple sclerosis.
The mechanism underlying the therapeutic activity of Cop 1 in MS has been extensively studied. Cop 1 was found to be immunologically cross-reactive with myelin basic protein (MBP), the main autoantigen in EAE and MS. Its suppressive effect results from several mechanisms, such as inhibition of the autoreactive pathogenic T-cells on one hand (Teitelbaum et al., 1988), and stimulation of suppressor cells on the other hand (Aharoni et al., 1993). The first step essential for the activation of these specific processes is the binding of Cop 1 to the histocompatibility molecules. Indeed, it has been shown that Cop 1, in two different batches of molecular weight 5,550 and 8,600, and relative molar ratio of L-Ala (4.1–5.8 residues), L-Glu (1.4–1.8 residues), L-Lys (3.2–4.2 residues) and L-Tyr (1 residue), binds very efficiently to a variety of MHC class II molecules of mouse and human origin, and furthermore competes with MBP and its major epitope p84-102 for MHC binding and can even displace such antigens that had already been bound to the MHC molecule (Fridkis-Hareli et al., 1994).
Mixed lymphocyte reaction (MLR) which is used clinically to assess immune rejection between donors and recipients was inhibited by Cop 1 (Schlegel et al., 1996). Cop 1 prevents GVHD in a murine model of lethal GVHD, which mimics MHC matched bone marrow transplantation in human (Schlegel et al., 1996). Thus, post transplantation administration of Cop 1 over a limited time after transplantation significantly reduced the incidence onset and severity of disease, resulting in improved long-term survival. Studies on the effect of Cop 1 on various processes involved in the pathological course of immune rejection showed that Cop 1 inhibited T cell proliferation in response to host cell (Aharoni et al., 1997). Cop 1 treatment completely abolished cytotoxic activity toward grafts, prevented the pro-GVHD IL-2 and IFN-γ cytokine secretion, and induced beneficial Th2 anti-inflammatory response. In view of these cumulative data, Cop 1 is a candidate drug for the prevention of GVHD in humans. See WO 96/32119 and U.S. Pat. No. 5,858,964.
None of the prior art publications describes or suggests that Cop 1 may be used to prevent or to treat HVGD, nor that there are other copolymers useful for preventing or treating GVHD or HVGD.
The nomenclature GLAT copolymer or YEAK copolymer has also been used for Cop 1. Thus, hereinafter in the specification and in the claims, the terms Copolymer 1, Cop 1, L-GLAT and L-YEAK will be used interchangeably for the L form of Cop 1, and the terms D-Copolymer 1, D-Cop 1, D-GLAT and D-YEAK will be used interchangeably for the D form of Cop 1.